EARLY HISTORY OF THE GERM-XUCLEI 



273 



nection with the reduction-problem ; and some of these have raised 

 some remarkable questions regarding the origin of reduction. A 

 large number of observers are now agreed that during the growth- 

 period preceding the maturation-division (p. 236),. in both sexes, the 

 nucleus of the mother-cell (spermatogonium, oogonium), both in 

 plants and in animals, passes through some of the changes prepara- 

 tory to reduction at a very early period. Thus, in the egg the pri- 

 mary chromatin-rods are often present in the very young ovarian 

 eggs, and from their first appearance are already split longitudinally. ^ 

 Hacker ('92, 2) made the interesting discovery that in some of the 

 copepods {CantJtocauiptiis, Cyclops) these double rods could be traced 



Fig. 136. — Longitudinal section through the ovary of the copepod Canthocamptus. [H.icKER.] 

 og. The youngest germ-cells or oogonia (dividing at og.'^) ; a. upper part of the growth-zone; 

 oc. oocyte, or growing ovarian egg; crj. fully formed egg, with double chromatin-rods. 



back continuously to a double spireme-thread, following immediately 

 upon the division of the last generation of oogonia, and that at no 

 period is a true reticniiini fonucd in the germinal vesicle (Fig. 136). 

 In the following year Ruckert('93, 2) made a precisely similar discov- 

 ery in the case of selachians. After division of the last generation 

 of oogonia the daughter-chromosomes do not give rise to a reticu- 

 lum, but split lengthwise, and persist in this condition throughout 

 the entire growth-period of the Qg^. Riickert therefore concluded 

 that the germinal vesicle of the selachians is to be regarded as a 

 " daughter-spireme of the oogonium {Ur-ei) grown to enormous 

 dimensions, the chromosomes of which are doubled and arranged in 



1 Hacker, Vom Rath, Ruckert, in copepods; Ruckert in selachians; Born and Fick in 

 Amphibia; HoU in the chick; Ruckert in the rabbit. 



